Models for Fault Behavior Elastic Rebound: Pre-earthquake strain is gradual in space and time Earthquake strain is abrupt in space and time Author: Mike Brudzinski

Our Classic View of Fault Behavior A New View of Fault Behavior Fast Slip Earthquake (minutes) Slow Slip Tremor (days) I’m going to start by using some simple animations to contrast our classic view of fault behavior with new views that have emerged through EarthScope. This shows a cross-section of subduction zone fault, like the one that caused the devastating Indian Ocean Earthquake and Tsunami in 2004. It shows the displacement that occurs at the surface of the earth leading up to an earthquake that releases the accumulated strain. The earthquake represents fast slip that produces energy release on the scale of minutes, as seen on this network of seismometer recordings. In the past few years we’ve learned a lot more about another type of fault behavior that we call slow slip. In this case the release of accumulated strain takes place gradually over many days and is accompanied by a subtle seismic tremor. This plots shows the tremor waxing and waning over the course of a day, whereas small earthquakes are these thin vertical lines.

Episodic Tremor and Slip Discovered in 2003, observations near Vancouver revealed the correlation in time and space of GPS detected slow slip (top) and tremor vibrations (bottom) These episodes typically last 2 weeks and recur in this region nearly every 14 months Rogers and Dragert, 2003

Cross-Section of Fault Behavior Dragert et al., 2000 What kind of fault is this? Shallow fault: Locked -> Earthquakes Deeper fault: Transition -> Tremor and Slip Changes in temperature and dehydration affect frictional properties of fault Thrust fault!

Sumatra, Indonesia Aftershocks Locked Fault Dec. 26, 2004 event Mar. 28, 2005 event Earthquakes from 1964-2004

This Is Why It Is Important Sumatra Cascadia